c++ - Swift 并使用 &int 参数调用 C++ 函数

Question

我研究了如何在一个项目中将 C++ 与 Swift 结合使用。

我有带接口(interface)的C++类

class SwypeDetect {
public:
  SwypeDetect();
  void asyncFunction(int &a);
};

和实现

SwypeDetect::SwypeDetect() {}

void SwypeDetect::asyncFunction(int &a) {
  a = 1;
  sleep(3);
  a = 10;
  sleep(3);
  a = 100;
}

asyncFunction 只是每三秒更改参数 a 的值三次。当然，我创建了 Objective-C 包装器

@interface Wrapper()
@property (nonatomic, assign) SwypeDetect detector;
@end

@implementation Wrapper

- (instancetype) init {
  self = [super init];
  if (self) {
    _detector = SwypeDetect();
  }
  return self;
}

- (void)asyncFunction:(int *)a {
  _detector.asyncFunction(*a);
}

@end

然后在 Swift 类中使用这个包装器

class ViewController: UIViewController {

  let queue = DispatchQueue(label: "wrapper queue", attributes:.concurrent)

  var valueA: Int32 = 0 {
    didSet {
      print("new valueA \(valueA) on time \(Date())")
    }
  }

  var detector: Wrapper? {
    didSet {
      if let detector = detector {
        queue.async {
          detector.asyncFunction(&self.valueA)
        }
      }
    }
  }

  override func viewDidLoad() {
    super.viewDidLoad()    
    detector = Wrapper()
  }
}

我预计 valueA 的 didSet block 会被调用三次，但在控制台中我只看到最后一次更改 valueA 的调用:“new valueA 100 on time 2018-03-26 11:50:18 +0000”。我可以做些什么来改变这种行为？

Answer 1

您必须在某处说“变量已更改”。例如，您可以使用闭包/ block /lambda 来完成

ViewController.swift

import UIKit

class ViewController: UIViewController {

    let queue = DispatchQueue(label: "wrapper queue", attributes:.concurrent)

    var valueA: Int32 = 0 {
        didSet {
            print("new valueA \(valueA) on time \(Date())")
        }
    }

    var detector: Wrapper? {
        didSet {
            if let detector = detector {
                queue.async {
                    detector.asyncFunction(&self.valueA) { value in
                        print("iteration value: \(value)")
                    }
                }
            }
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        detector = Wrapper()
    } }

Wrapper.h

#import <Foundation/Foundation.h>


@interface Wrapper : NSObject
- (instancetype) init;
- (void)asyncFunction:(int *)a progressHandler: (void(^)(int))progressHandler;
@end

Wrapper.mm

#import "Wrapper.h"
#import "SwypeDetect.hpp"

@interface Wrapper()
@property (nonatomic, assign) SwypeDetect detector;
@end

@implementation Wrapper

- (instancetype) init {
    self = [super init];
    if (self) {
        _detector = SwypeDetect();
    }
    return self;
}

- (void)asyncFunction:(int *)a progressHandler: (void(^)(int))progressHandler {
    _detector.asyncFunction(*a , progressHandler);
}

@end

SwipeDetect.cpp

#include "SwypeDetect.hpp"
#include <unistd.h>
#include <iostream>
SwypeDetect::SwypeDetect() {}

void SwypeDetect::asyncFunction(int &a, std::function<void(int)> f) {
    std::cout << "Come up and C++ me some time." << std::endl;
    a = 1;
    f(a);
    sleep(1);
    a = 10;
    f(a);
    sleep(1);
    a = 100;
    f(a);
}

SwypeDetect.hpp

#include <stdio.h>
#include <functional>
class SwypeDetect {
public:
    SwypeDetect();
    void asyncFunction(int &a, std::function<void(int)> f);
};

测试集set-Bridging-Header.h

#import "Wrapper.h"